Tool bars are pulled by tractors to cultivate soil, plant seeds in the ground, and apply fertilizer, herbicides, insecticides, and fungicides. To improve efficiency, reduce cost per acre, and reduce soil compaction, the width of an area planted during each pass through a field has been increased. Tool bars are available that can plant thirty-six rows of corn with a space of thirty inches between rows. The tool bar must have a length of about ninety feet to carry thirty-six planter units with thirty inch row spacing. A tool bar that is capable of carrying 36 planter units and planting thirty-six rows of corn simultaneously with thirty inches between rows must have some flexibility to follow the field surface contour even when planting in fields that have been leveled by laser controlled earth movers. Each planter unit is attached to a tool bar by a linkage that permits the unit to float up and down relative to the tool bar. A depth control system, that is part of each planter unit, controls the depth that seeds are deposited below the surface of soil. Seeds are ideally planted at a uniform depth so that they germinate and emerge at about the same time. The total depth depends on factors such as soil type, moisture content, soil temperature and a farmer's educated assessment based on years of experience. It is generally considered desirable to position the seeds that are the deepest within one inch of seeds that are closest to the surface. If the tool bar is too high, it will tend to lift a planter unit. If the tool bar is too low, it will tend to force a planter unit downward and increase seed depth.
Seed depth is more uniform if a tool bar has a center section and wing sections pivotally attached to the center section. The center section is supported by gauge wheels that are spaced outward from the center of the center section. The wings have inboard ends that are pivotally attached to adjacent end of the center section for pivotal movement about a horizontal fore and aft extending axis. Each wing section has a gauge wheel or gauge wheels that are mounted on the wing section outboard portion. The horizontal fore and aft extending axis should be as low as possible to minimize the change in row spacing between a planter unit on an outboard end of the center section and the planter unit on an inboard end of the wing section.
A tool bar for simultaneously planting thirty-six crop rows with thirty inch row spacing will typically have twelve planter units on the center section, twelve planter units on the left wing, and twelve planter units on the right wing. The center section of the tool bar with twelve planter units set to provide thirty inch spacing between rows of plants is too wide to move on some rural roads.
The width of the center section is reduced by attaching two planter units, on the left end of the center section, to the left wing and attaching two planter units, on the right end of the center section to the right wing when folding the wings forward to transport on rural roads. The eight planter units that remain with center section can be moved short distances on rural roads.
A telescopic tongue includes a rear portion that is attached to the center section and a forward portion that carries a hitch assembly. During planting or other operations in a field, the length of the telescopic tongue is reduced to make it easier to change the direction of forward movement. When the wings are folded to the front for movement between fields or into a storage building for example, the length of the telescopic tongue is increased to make room for the outboard ends of the wing sections. In the folded transport position, the wing sections are supported by the telescopic tongue.
A towing tractor exerts tension forces on the telescopic tongue when pulling the tool bar in the field as well as when pulling the tool bar in a forward folded transport position. The pulling tension when the telescopic tongue is extended is transmitted from a front tongue beam to a rear tongue beam by left and right tension connector links that limit the maximum length of the telescopic tongue. The tension connector links provide a longer unit than necessary when the wings are folded for movement between fields. Locks of various descriptions have been employed to lock the telescopic tongue in a retracted position during tilling and planting operations. Some of the locks have been too weak. Other locks have employed complicated linkages that require close inspection to insure that the lock is engaged. Hydraulically operated locks employing a dedicated hydraulic circuit have also been used. The hydraulic cylinder may require an additional hydraulic control valve. The number of control valves and hydraulic couplers on tractors are limited. The tools attached to a tool bar may require more hydraulic circuits than some tractors have.